Agkistrodon contortrix mokasen
Johnson Co., Illinois. May 2nd, 1998
The mokasen found down in southern Illinois are probably a blend of the Southern and Northern copperhead gene pool; often it is difficult to be distinctive where two subspecies meet. Most coppers from this area show the dark spots on the light between crossbands, typical of the northern subspecies, and even so some show the more pinched or even broken crossbands of the southern form.
NOTE: I have not followed the Agkistrodon synonomies of Burbrink & Guiher 2014, pending further studies making use of appropriate sample sizes.
HerpMapper records for this species are here.